A known conventional variable valve-operating device disclosed, for instance, by Japanese Patent Laid-open No. 2004-100555 mechanically changes the valve lift amount and valve timing in accordance with the operation of an internal combustion engine.
In the variable valve-operating device disclosed by Japanese Patent Laid-open No. 2004-100555, a camshaft is provided with two rotary cams, and a first rotary cam opens/closes a first intake valve of two intake valves positioned in a cylinder whereas a second rotary cam opens/closes a second intake valve. A variable valve transmission mechanism, which comprises a four-bar linkage, is positioned between the first rotary cam and first intake valve and between the second rotary cam and second intake valve.
The four-bar linkage for the above variable valve-operating device comprises an input arm, which has an input section that comes into contact with a rotary cam; a transmission arm, which is coupled to the input arm in a swingable manner; a swing arm, which is coupled to the transmission arm in a swingable manner, is capable of swinging around a rotary control shaft, and transmits a driving force, which is transmitted from a rotary cam, to an output section that opens/closes an intake valve; and a control arm, which rotates around the rotary control shaft and is coupled to the input arm in a swingable manner. The operating characteristic of an intake valve can be mechanically changed by controlling the attitude of the four-bar linkage to change the positional relationship between a rotary cam and input section.
Further, the above variable valve-operating device includes a coupling mechanism, which couples the four-bar linkage (first linkage) for the first intake valve to the four-bar linkage (second linkage) for the second intake valve, and a mechanism for maintaining the second linkage's attitude for providing the maximum operating angle of the second intake valve when the first and second linkages are uncoupled. The coupling mechanism comprises a through-hole, which is formed in the control arm of each four-bar linkage, and a coupling pin, which is to be inserted into the through-hole. The mechanism for maintaining the second linkage's attitude at the time of uncoupling comprises a through-hole that is formed in a stationary plate, a through-hole that is formed in the control arm (second control arm) of the second linkage, and the above-mentioned coupling pin.
The coupling pin is constantly engaged with the through-hole in the second control arm. The coupling pin can move toward the control arm (first control arm) of the first linkage and toward the stationary plate while it is engaged with the through-hole in the second control arm. When the coupling pin moves toward the first control arm and becomes inserted into the through-hole in the first control arm, the second control arm is coupled to the first control arm via the coupling pin. When the control arms are coupled, the first and second linkages assume the same attitude at all times. In this instance, control can be exercised so that the first and second valves have the same operating characteristic.
On the contrary, when the coupling pin moves toward the stationary plate and becomes inserted into the through-hole in the stationary plate, the second control arm is coupled to the stationary plate via the coupling pin. When the second control arm and stationary plate are coupled, the attitude of the second linkage is fixed. When the attitude of the first linkage is controlled to change the positional relationship between a rotary cam and input section, only the operating characteristic of the first valve can be mechanically changed with the operating characteristic of the second valve remaining unchanged.
In other words, the above variable valve-operating device can selectively provide the first and second intake valves with the same operating characteristic or with different operating characteristics. In this manner, the operating characteristics of the first and second intake valves, particularly, the lift amounts of these valves, can be rendered different from each other. Therefore, different intake flow rates can be employed to invoke a swirling flow within a combustion chamber. This makes it possible to provide stable combustion in the combustion chamber.